This application relates to wireless communication systems and techniques based on orthogonal frequency division multiplexing (OFDM) and orthogonal frequency division multiple access (OFDMA), and the multicast/broadcast services over OFDM/OFDMA wireless networks.
Wireless communication systems use electromagnetic waves to communicate with wireless communication devices located within cells of coverage areas of the systems. A radio spectral range or band designated or allocated for a wireless communication service or a particular class of wireless services may be divided into different radio carrier frequencies for generating different communication frequency channels. This use of different frequencies for different communication channels may be used in various multiple access radio wireless communication systems.
OFDM and OFDMA systems generate different channels within a given band by using the orthogonal frequency division multiplexing to generate channel spectral profiles that are orthogonal to one another without interference when different channels are centered at selected equally-spaced frequencies. Under the OFDM, the frequency spacing can be smaller than the minimum spacing in conventional channels and hence increase the number of channels within a given band. The existing and developing specifications under IEEE 806.16x standards support wireless communications under OFDM and orthogonal frequency division multiple access (OFDMA). The drafts for IEEE 806.16 published in January 2004 and revised in December 2005 (802.16d/Corl revision D5 and 802.16e revision D12) provide detailed technical specifications for OFDM and OFDMA wireless systems.
Similar to other wireless communication systems, OFDM and OFDMA wireless systems support point-to-point transmission of data where a base station (BS) transmits data to a subscriber station (SS) via a downlink traffic channel on a per burst basis. To obtain optimal system performance, the BS selects the best burst profile at each transmission time based on a channel condition feedback sent by the SS. A burst profile is a set of parameters that describes transmission properties and may include parameters such as the modulation type, forward error correction (FEC) type, etc.
In addition to the point-to-point transmission, OFDM and OFDMA wireless systems may also be configured to support Multicast/Broadcast service (MBS) that allows for unidirectional point-to-multipoint transmission of multimedia data (e.g. text, audio, picture, video) from a single source point to a multicast group of multiple receivers in a multicast area. As an example, the text data in MBS may include weather forecast information, traffic reports, and short messages. In some implementations, OFDM and OFDMA wireless systems may be configured to support MBS data transmission on the downlink. Data for a MBS connection is transmitted by the BS over a single shared traffic channel and received by multiple SSs.
In MBS, different SSs receive the single MBS channel and may experience different receiving conditions. Hence, for the same MBS channel, different receiving SSs may experience different bit errors. Unlike the point-to-point transmission, the nature of the MBS does not allow for error connection via automatic repeat request (ARQ) or hybrid ARQ for individual receiving SSs. Therefore, there is a need for an efficient feedback mechanism in the uplink from each SS to the BS in a MBS connection to allow the BS to configure the burst profile of the downlink MBS connection with sufficient large downlink transmission capacity and reduced latency while maintaining the bit errors within the acceptable level for the MBS service.